Byzantium/Constantinople was conquered in 1451, but the empire continued to decline starting around the 18th or 19th centuries. It officially died in WWI. As for how long it was a major threat to Europe, the empire's prime was the 16th century, under Suleiman the Magnificent.
One reason factory owners employed children because they were significantly cheaper than hiring an adult. "the child is paired one shilling or one shilling and six pence". This shows that it's more cost efficient to hire a child.
Another reason factory owners employed children because of their size. Here is a quote to support this "The smallest child in the factories were scavengers they go under the machine". This shows that if the child is smaller they can do more dangerous jobs than an adult.
A lodeing dock where the lodes the raw materials either for trade or for resorce payment
To answer your first question, social darwinism is a theory that supports the rich getting richer. Republican party is based around this theory. Since they believe that those who are the fittest get the money, there is no reason to help the poor, because that is their fault. We can also attach to this the theory of mercantilism where everyone get what they truly deserve. On the other hand, social gospel movement is a christian movement that wanted to help the poor based on christian values. This movement applied christian ethics to social problems such as poverty, delinquency, racism, child labor and so on.
